The present invention relates to optical waveguides for carrying optical signals, or causing optical signals to resonate. More specifically, the invention relates to solid state optical waveguides which provide gain or amplification to the optical signals being carried there through.
Typically an optical waveguide is comprised of a thin film of material deposited upon a substrate. This material is then etched or altered to form a waveguide path.
Optical waveguides are becoming increasingly popular, specifically in the fields of communications optical circuits and resonators. Furthermore, optical waveguides may be used for any application which requires the transmission of optical signals from one point to another.
Optical waveguides may be easily configured to form resonators. Resonators can be created by configuring the optical waveguide in a closed loop path and injecting or coupling light beams therein. Due to the closed loop configuration of the waveguide path, the light within the path is caused to resonate within the closed loop. These closed loop resonators are useful for rotation sensing in passive cavity gyroscopes.
Propagation loss within the waveguide is a very important parameter which will effect efficiency and operation. Generally, optical waveguides are very low loss devices. However, it is desired to create a lower loss, more ideal optical waveguide. While many waveguides are presently very low loss devices, propagation loss is still a problem for many applications, including long haul transmission and closed loop resonators. Due to propagation losses there is a need to provide amplifiers or boosters which will increase the amplitude of the signals to account for propagation losses within the waveguide.
Much work is being done in the field of signal transmission to provide amplifiers within a waveguide transmission system. These amplifiers are especially important when transmitting signals over large distances.
As previously mentioned, in the field of rotation sensing a resonator can be used to detect rotation. In a closed loop resonator, light beams travel around the closed loop. If this loop is rotated, the frequency of the resonant signals are shifted. However, in order to create a rotation sensor using these principles, it is necessary to have a very low loss resonator with amplification capabilities, thus allowing the resonant light to maintain itself for long periods of time.
In the fields of communication signal transmission and rotation sensing, work is presently being done with fiber optic cables. Again, fiber optic cables experience problems due to propagation loss and thus reduce their efficiency and effectiveness for carrying signals over long large distances. Therefore, work is presently being done to provide fiber optic cables with periodic amplifiers to amplify the signals being transmitted there through. One attempted method of providing amplification has been to dope the fiber optic cable with rare earth materials and optically pump these materials to create population inversion which can amplify light. The rare earth materials used include erbium, neodymium, and praseodymium. Many problems have been encountered with this technique however, causing the desired amplification to be ineffective. One big problem involves the clumping of material within the glass fiber when doped. The doped material clumps together rather than uniformly distributing itself within the glass fiber. This clumping causes the propagation loss to increase.
With optical waveguides the method used to fabricate the waveguide is very important. Impurities within the guide will increase the propagation losses. Therefore it is necessary to create waveguides which are free of impurities. Furthermore, irregularities in the waveguide will also increase propagation loss. Maintaining a uniform thickness is therefore very important. The process used to fabricate the waveguide must be capable of controlling both thickness and purity of the resulting waveguide. Also, when doping one material with a dopant, it is important that the process used be capable of performing this doping to result in uniform, dense distribution of the dopant.
An effective method of amplifying signals within optical waveguides has not yet been developed. Therefore, at the present time it is not possible to produce an efficient low loss waveguide that has amplifying characteristics.